The present invention relates to a beyond-center locking toggle mechanism for automatically operating the breach block of a firearm and, more particularly, to such a mechanism which is driven with a minimum of parts by positive mechanical action throughout its travel, despite the fact that its operation is initiated by the gas pressure associated with a fired projectile.
Numerous automatic breach block withdrawal actions have been designed for firearms, particularly for pistols, utilizing an over- or under-center locking toggle linkage connected to the breach block. Such beyond-center locking toggle linkages can provide positive locking of the breach block into position for firing, while allowing a relatively simple withdrawal thereof to permit ejection of a shell and loading of a new one. U.S. Pat. Nos. 2,069,432 and 3,783,739 issued respectively to Watanabe and Perrine, disclose actions of this type. Such locking toggle actions typically have drawbacks which have prevented toggle linkages from being adopted to any appreciable degree. For example, most present designs, including the Watanabe and Perrine designs, rely on the back pressure generated within the barrel of the firearm acting against the breach block to urge such breach block into a withdrawn position once the toggle lock is broken. This utilization of the back pressure reduces the momentum imparted to the bullet or other projectile being fired, thus reducing the range and effectiveness of the firearm. Moreover, such back pressure is caused by the gas products resulting from the explosion of powder, which gas products flow into the breach operating mechanism if the pressure of the same is used to move the breach block. These products will build up over a period of time within the breach block operating mechanism and other movable parts of the firearm, causing malfunctions.